Conventionally, a cooling process executed by a cooling system using a cooling medium of an air-conditioner or by a cooling system of a gasoline engine of an automobile, particularly a large automobile, is executed by using a heat exchanger, which is forcibly cooled down by revolving a fan if necessary.
The driving control of a motor for revolving a fan blade is performed with a simple control method for turning on/off a driving circuit of the motor on the basis of a temperature detection signal from a temperature sensor (a water temperature sensor or the like in the case of a gasoline engine) of a heat exchanger.
If the motor being used is a brush motor, a controller of a fan motor can control the number of revolutions with an effective voltage. In this case, pulse width modulation (PWM) control using a semiconductor is used. With the pulse width modulation (PWM) control, the number of revolutions of a fan motor can be smoothly controlled by varying a time width (duty ratio) of ON to OFF.
For such a control, a control unit is used. The control unit side has a protection function for decreasing an electric current to a safe range as a protection operation performed when, for example, a temperature within the unit is high or an anomalous current flows, due for example to locking of a fan motor, in addition to controlling the number of revolutions of the fan motor according to a temperature of a cooling medium of a heat exchanger.
Incidentally, with improvements in fuel efficiency in automobiles, engines have been increasing in power consumption as well as in size. As the power consumption increases, current becomes higher. This can pose a more serious problem when a fault occurs than conventional engines. Accordingly, system protection priority control such as multi-step control, more precise revolution speed control, or the like has been performed in recent years in order to perform a more precise revolution control of an engine.
With such a system protection priority control, when for example a temperature sensor arranged in an engine cooling system detects an anomaly, an electric fan control device for cooling down an engine ignores control performed for an electric motor according to another control, and continues to cool down the engine by driving the electric motor with a maximum number of revolutions, or continues to drive the electric motor with a controlled number of revolutions corresponding to normal conditions where a temperature detected by the temperature sensor is low (for example, see Patent Document 1).
FIG. 10 is a block diagram simply illustrating a configuration of such an electric fan control device for cooling down an engine. As illustrated in this figure, an electric current of a power supply battery 1 is supplied to a motor 2 for revolving and driving the engine cooling fan, not illustrated, and to a motor control device 3 (engine cooling electric fan control device) for controlling the number of revolutions of the motor 2.
The motor control device 3 has a controller 4 and a switching element 5. The controller 4 causes the motor 2 to revolve at a predetermined temperature or higher on the basis of an externally input control signal 6 (such as a temperature detection signal from a temperature sensor arranged in a heat exchanger of an engine cooling system, or information from another control unit), and outputs a PWM (Pulse Width Modulation) control signal for controlling the number of revolutions of the motor 2 according to a temperature.
The switching element 5 has a continuously closed contact part and a pulse control unit. The switching element 5 has a function for controlling the number of revolutions of the motor 2 by turning on/off a current on the basis of the control signal from the above described controller 4, and for decreasing the temperature of a cooling medium of the heat exchanger by revolving a fan, not illustrated.
Additionally, the electric motor is driven with a controlled number of revolutions, corresponding to a case where a detected temperature of the temperature sensor is low according to the control of the controller 4. Cooling of the engine by driving the electric motor with a maximum number of revolutions while ignorant of a control performed by another device for the electric motor can be easily maintained by shorting the circuits of the positive and negative poles within the switching element 5.